Electronic components have become diversified in recent years, entailing the need for high-speed and highly accurate mounting of electronic components on printed circuit boards. Therefore, for high-speed and highly accurate mounting of electronic components on printed circuit boards, it is necessary to transfer and place printed circuit boards in prescribed positions quickly and with high accuracy.
Conventional apparatuses for transferring and positioning printed circuit boards in prescribed positions include what is shown in FIG. 4. This transfer apparatus 20 comprises such driving units as transfer rails 22, on which a printed circuit board 21 is to be transferred and guided; a vertically movable hook 23 disposed beside one of the transfer rails 22; a mechanism 24 for moving the hook 23 up and down; a guide rail 25 for guiding the hook 23 back and forth in parallel with the transfer rails 22; and a cylinder unit 26 for moving the hook 23 back and forth along the guide rail 25. The hook 23 is engaged in an engaging hole 27 formed in the printed circuit board 21, and the driving units are driven to move the hook 23 along the guide rail 25 to transfer and place the printed circuit board 21 in a prescribed position.
However, the above-described conventional transfer apparatus 20 requires, separately from the transfer rails 22, driving units for moving the hook 23 in parallel with the transfer rails 22; the mechanism 24 for moving the hook 23 up and down; and the guide rail 25 for moving the hook 23 back and forth in parallel with the transfer rail 22, resulting in a greater size and complexity of the whole apparatus. This leads to problems regarding costs and installation space, and the printed circuit board 21 itself requires the engaging hole 27 for engaging the hook 23, which limits the range of usable printed circuit boards 21.
In this connection, there is also available, as shown in FIG. 5, a transfer apparatus provided with a conveyor belt 30 for guiding and transferring a printed circuit board 21 seated thereon is disposed on a frame 31 via a belt-driving unit 32, and a stopper 33 for placing the printed circuit board 21 in a prescribed position, whereby the printed circuit board 21 is seated on the conveyor belt 30 and transferred to the stopper 33 by running the belt-driving unit 32.
This transfer apparatus 20 can transfer the printed circuit board 21 in a simple configuration, but, if the conveyor belt 30 is run too fast when it transfers the printed circuit board 21, the printed circuit board 21 may fail to be positioned exactly where it should be or electronic components mounted thereon may be dislocated or damaged by any impact that may occur when the printed circuit board 21 hits the stopper 33 even if it comes into contact with the stopper 33 in the prescribed position.
In order to solve the above-mentioned disadvantages, another apparatus is available, which effects control to lower the transfer speed of the conveyor belt 30 before the printed circuit board 21 hits the stopper 33.
This can ease the impact of the printed circuit board 21 hitting the stopper 33 and also restrain the dislocation of, or the occurrence of defects in, the electronic components. However, because the printed circuit board 21 and the conveyor belt 30 are in frictional contact with each other, if a slip occurs between the printed circuit board 21 and the conveyor belt 30, the printed circuit board 21 cannot slow down to the level of the lowered speed of the conveyor belt 30, with the possible result that the printed circuit board 21 hits the stopper 33 with an unnecessarily great impact or, conversely, the printed circuit board 21 may be transferred at a lower speed than the conveyor belt 30, taking too long a transfer time. Either trouble makes it difficult to realize high-speed transfers of the printed circuit board 21.